In general, complex-shaped fluororubber formed products, such as primer valve and bellows-structured flexible joints, expansion joints, boots, and grommets, are formed by heating and thereby cross-linking and molding a rubber composition with a mold corresponding to the complex shape. In releasing the product from the mold, however, cross-linked products are damaged in some cases due to the complex shape.
Fluororubbers are known to be excellent in chemical resistance, oil resistance, and heat resistance, and to have good resistance to compression set (for example, see Patent Documents 1 and 2). Common cross-linked products of fluororubber, however, are not as excellent in mechanical properties at high temperatures as those of non-fluororubber. Thus, the complex-shaped fluororubber formed products are disadvantageously likely to be damaged when they are produced.    Patent Document 1: JP 60-55050 A    Patent Document 2: JP 9-124871 A